The present invention relates to a silica-polymer composite, more particularly relates to a silica-polymer composite with a low viscosity during mixing with rubber, a good processability, and superior dispersibility. Further, the present invention relates to a rubber composition containing that silica-polymer composite.
A rubber composition comprised of an amino group-containing diene-based rubber and silica is known from Japanese Unexamined Patent Publication (Kokai) No. 64-22940, WP96/30444, Japanese Unexamined Patent Publication (Kokai) No. 9-151275, and Japanese Unexamined Patent Publication (Kokai) No. 9-151276, etc. Further, the method of producing a master batch by coprecipitating a silicate and latex is known from Japanese Patent No. 1146028. Further, the method of producing a rubber-silica reinforced master batch using a silane coupling agent is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-231381. Further, U.S. Pat. No. 3,098,837 discloses a composite of butadiene-2-methyl-5 vinyl pyridine copolymer and silica. For the method of synthesis, however, it is indicated that careful control of the pH is required and that control of the drying temperature is also required.
Further, U.S. Pat. No. 4,481,328 discloses a composite of a butadiene-methacrylate copolymer and carbon black.
An object of the present invention is to provide a silica-polymer composite which coagulates without separation of the silica and polymer by reacting the silica with a specific polymer having a polar ring and benzene ring or a specific polymer having a specific carboxylic acid.
Another object of the present invention is to provide a rubber composition comprised of a blend of this composite and a rubber and having a good processability and superior uniform dispersibility of the silica.
According to a first aspect of the present invention, there is provided a silica-polymer composite obtained by reacting a polymer having a polar group containing a hetero atom and a benzene ring with silica in a solution.
Preferably, the silica is treated with the polymer having the pyridine ring and benzene ring in the molecule in a solution and then treated by another polymer solution.
According to a second aspect of the present invention, there is provided a rubber composition containing such a silica-polymer composite.
Further, according to a third aspect of the present invention, there is provided a method of producing a silica-polymer composite comprising reacting a polymer having a polar group containing a hetero atom and a benzene ring with silica in a solution.
According to a fourth aspect of the present invention, there is provided a silica-polymer composite obtained by reacting a polymer having a carboxylic acid with silica.
According to a fifth aspect of the present invention, there is provided a rubber composition containing such a silica polymer composite.
According to a sixth aspect of the present invention, there is provided a method of producing a silica-polymer composite comprising reacting a polymer having a carboxylic acid with silica.
Silica exhibits good viscoelastic characteristics in combination with rubber, but is inferior in dispersibility. It is known to improve the dispersibility of silica using various methods so as to further improve the viscoelastic characteristics. On the other hand, emulsion-polymerized SBR is more advantageous in cost than solution-polymerized SBR and further has the advantage of being superior in dynamic properties. Therefore, the present inventors etc. experimented with using emulsion polymerized SBR to make a master batch, whereupon they discovered that by treating the silica with one of the types of polymers used in the present invention, especially, a vinyl pyridine-containing SBR latex, it was possible to synthesize a composite free from separation of the silica and rubber without control of the pH or control of the drying temperature. This is believed to be due to the aggregation force between benzene rings. Further, the present inventors discovered that it is possible to synthesize a composite free from separation of the silica and rubber even when adding a SBR latex and causing coagulation after adding the vinyl pyridine-containing SBR latex to the silica. Further, since the obtained composite is low in viscosity during kneading with rubber, excellent in processability, and superior in dispersibility as well, it is extremely useful as a master batch for blending of reinforcing silica in rubber compositions.
Further, the inventors discovered that by similarly treating silica by a carboxylic acid-containing latex, it is possible to synthesize a composite without separation of the silica and rubber. Further, they discovered that a surfactant could be used and that colloidal silica could be effectively used as the silica. Further, they discovered that the composite obtained was excellent in processability and superior in dispersibility and a rubber composition containing this was high in tensile strength.
In the present invention, as the polymer having a polar group containing a hetero atom and a benzene group to be reacted with the silica in a solution, typically a diene-based rubber latex having a polar group containing a hetero atom and a benzene ring is used. In the present invention, it is effective if a diene-based rubber latex having a polar group containing a hetero atom and a benzene ring or that diene-based rubber latex having a polar group and a benzene ring and another diene-based rubber latex are used together, since a rubber composition is obtained which has a high degree of balance in the heat buildup, tensile strength, abrasion resistance, processability, and other characteristics.
As he hetero atom, atoms belonging to Group 5B and Group 6B of the second to fourth Periods of the Periodic Table are shown. Specifically, for example, a nitrogen atom, oxygen atom, sulfur atom, phosphorus atom, etc. may be mentioned. Among these, a nitrogen atom, oxygen atom, etc. are preferred.
As he polar group containing such a hetero atom, for example, a hydroxyl group, alkoxysilyl group, epoxy group, carboxyl group, carbonyl group, oxycarbonyl group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, imino group, amino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, oxygen-containing heterocyclic group, nitrogen-containing heterocyclic group, sulfur-containing heterocyclic group, etc. may be mentioned. Among these, a hydroxyl group, carboxyl group, epoxy group, sulfide group, sulfonyl group, amino group, nitrogen-containing heterocyclic group, alkoxysilyl group, etc. are preferred. A hydroxyl group, amino group, carboxy group, nitrogen-containing heterocyclic group, alkoxysilyl group, etc. are more preferred. A carboxyl group, amino group, nitrogen-containing heterocyclic group, alkoxysilyl group, etc. are most preferred.
As the polymer having a polar group containing a hetero tom and a benzene group, for example, (1) a polar group-containing diene-based rubber, such as a copolymer of a vinyl-based monomer having a polar group containing a hetero atom, a conjugate diene, and an aromatic vinyl compound or (2) a diene-based rubber containing a polar group comprising a copolymer of a conjugate diene and an aromatic vinyl compound, wherein the (co)polymer having an active metal bonded in the molecule is reacted with a modifying agent to introduce a polar group containing a hetero atom into the (co)polymer.
The content of the monomers in the diene-based rubber containing a polar group obtained by copolymerization of (1) as stated above may be suitably selected in accordance with the objective. In the case of a polymer (rubber) of a vinyl-based monomer having a polar group containing a hetero atom, a conjugate diene, and an aromatic vinyl compound, the content of the bonding units:of the polar group-containing vinyl-based monomer is normally 0.01 to 20 wt %, preferably 0.05 to 15 wt %, more preferably 0.1 to 10 wt %, the content of the bonding units of the conjugate diene monomer is normally 40 to 94.99 wt %, preferably 50 to 85 wt %, more preferably 55 to 80%, and the content of the bonding units of the aromatic vinyl monomer is normally 5 to 55 wt %, preferably 10to 45 wt %, more preferably 15 to 40 wt %. Further, when using a copolymer (rubber) latex having such contents of monomer bonding units, a rubber composition is obtained with a high degree of balance of the properties of the heat buildup and the wet skid resistance.
The contents of the monomers in the polar group-containing diene-based rubber into which a polar group containing a hetero atom is introduced by the above method of modification of (2) are suitably selected in accordance with the required properties. The content of the bonding units of the conjugate diene monomer is normally 40 to 100 wt %, preferably 50 to 90 wt %, more preferably 60 to 85 wt %, while the content of the bonding units of the aromatic vinyl monomer is normally 0 to 60 wt %, preferably 10 to 50 wt %, more preferably 15 to 40 wt %.
As the conjugate diene, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, isoprene, etc. may be mentioned. Among these, 1,3-butadiene, 2-methyl-1,3-butadiene, isoprene, etc. are preferred. 1.3-butadiene is more preferred. These conjugate dienes may be used alone or in combinations of two or more types.
As the aromatic vinyl monomer, an aromatic vinyl compound not having a polar group is used. For example, styrene, xcex1-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-diisopropyl-styrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene, monofluorostyrene, etc. may be mentioned. Among these, styrene is preferred. The aromatic vinyl monomer may be used alone or in combinations of two or more types.
Further, the polar group-containing vinyl-based monomer is not particularly limited so long as it is a polymerizable monomer having at least one polar group in its molecule. Specifically, for example, an amino group-containing vinyl-based monomer, a hydroxyl group-containing vinyl-based monomer, a carboxyl group- containing vinyl-based monomer, an alkoxysilyl group-containing vinyl-based monomer, etc. may be mentioned. Preferably, a carboxyl group-containing vinyl-based monomer, an alkoxysilyl group-containing vinyl-based monomer, an amino group-containing vinyl-based monomer, etc. may be mentioned. These polar group-containing vinyl-based monomers may be used alone or in combinations of two or more types.
As the amino group-containing vinyl-based monomer, a polymerizable monomer having at least one amino group selected from a primary, secondary, and tertiary amino group in its molecule may be mentioned. Among these, a tertiary amino group-containing vinyl-based monomer is particularly preferred. These amino group-containing vinyl-based monomers may be used alone or in combinations of two or more types.
As the primary amino group-containing vinyl-based monomer, for example, acrylamide, methacrylamide, p-aminostyrene, aminomethyl(meth)acrylate, aminoethyl(meth)acrylate, aminopropyl(meth)acrylate, aminobutyl(meth)acrylate, etc. may be mentioned.
As the secondary amino group-containing vinyl-based monomer, for example, the anilinostyrenes disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-130355; the anilinophenylbutadienes disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-130356; N-monosubstituted (meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-methylol acrylamide, N-(4-anilinophenyl)methacrylamide, etc.; etc. may be mentioned.
As the tertiary amino group-containing vinyl-based monomer, for example, N,N-disubstituted aminoalkylacrylate, N,N-disubstituted aminoalkylacrylamide, N,N-disubstituted amino aromatic vinyl compound, and a vinyl compound having a pyridine group may be mentioned.
As the N,N-disubstituted aminoacrylate, for example, N,N-dimethylaminomethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminobutyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, N,N-diethylaminobutyl(meth)acrylate, N-methyl-N-ethylaminoethyl(meth)acrylate, N,N-dipropylaminoethyl(meth)acrylate, N,N-dibutylaminoethyl(meth)acrylate, N,N-dibutylaminopropyl(meth)acrylate, N,N-dibutylaminobutyl(meth)acrylate, N,N-dihexylaminoethyl(meth)acrylate, N,N-dioctylaminoethyl(meth)acrylate, acryloylmorpholine, and other acrylic acid or methacrylic acid esters etc. may be mentioned. Among these, N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-dipropylaminoethyl(meth)acrylate, N,N-dioctylaminoethyl(meth)acrylate, N-methyl-N-ethylaminoethyl(meth)acrylate, etc. are preferred.
As the N,N-disubstituted aminoalkyl acrylamide, for example, N,N-dimethylaminomethyl(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-dimethyloaminobutyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N,N-diethylaminobutyl(meth)acrylamide, N-methyl-N-ethylaminoethyl(meth)acrylamide, N,N-dipropylaminoethyl(meth)acrylamide, N,N-dibutylaminoethyl(meth)acrylamide, N,N-dibutylaminopropyl(meth)acrylamide, N,N-dibutylaminobutyl(meth)acrylamide, N,N-dihexylaminoethyl(meth)acrylamide, N,N-dihexylaminopropyl(meth)acrylamide, N,N-dioctylaminopropyl(meth)acrylamide, and other acrylamide compounds or methacrylamide compounds etc. may be mentioned. Among these, N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N,N-dioctylaminopropyl(meth)acrylamide, etc. are preferred.
As the N,N-disubstituted amino aromatic vinyl compound, for example, N,N-dimethylaminoethylstyrene, N,N-diethylaminoethylstyrene, N,N-dipropylaminoethylstyrene, N,N-dioctylaminoethylstyrene, and other styrene derivatives may be mentioned.
Further, instead of an amino group, a nitrogen-containing heterocyclic group is also possible. As such a nitrogen-containing heterocyclic group, for example, pyrrole, histidine, imidazole, triazolidine, triazole, triazine, pyridine, pyrimidine, pyrazine, indole, quinoline, purine, phenazine, pteridine, melamine, etc. may be mentioned. The nitrogen-containing heterocyclic group may contain another heterocyclic group in the ring as well. Further, as a vinyl compound having a pyridyl group, for example, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine, etc. may be mentioned. Among these, 2-vinylpyridine, 4-vinylpyridine, etc. are preferred.
As the hydroxyl group-containing vinyl-based monomer, a polymerizable monomer having at least one primary, secondary, or tertiary hydroxyl group in its molecule may be mentioned. As such a hydroxyl group-containing vinyl-based monomer, for example, an unsaturated carboxylic acid-based monomer, vinyl ether-based monomer, vinyl ketone-based monomer, etc. all containing a hydroxyl group may be mentioned. Among these, a hydroxyl group-containing unsaturated carboxylic acid-based monomer is suitable. As a hydroxyl group-containing unsaturated carboxylic acid-based monomer, for example, an acrylic acid, methacrylic acid, itaconic acid, fumaric: acid, maleic acid, or other acid ester, amide, anhydride, or other derivative may be mentioned, in particular an acrylic acid, methacrylic acid, or other acid ester.
Further, as specific examples of the hydroxyl group-containing vinyl-based monomer, for example, hydroxymethyl(meth)acrylate, 2-hydroxyethyl-(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, 3-chloro-2-hydroxypropyl(meth)acrylate, 3-phenoxy-2-hydroxypropyl(meth)acrylate, glycerolmono-(meth)acrylate, hydroxybutyl(meth)acrylate, 2-chloro-3-hydryoxpropyl(meth)acrylate, hydroxyhexyl(meth)-acrylate, hydroxyoctyl(meth)acrylate, hydroxymethyl(meth)acrylamide, 2-hydroxypropyl(meth)acrylamide, 3-hydroxypropyl(meth)acrylamide, di-(ethyleneglycol)itaconate, di-(propyleneglycol)itaconate, bis(2-hydroxypropyl)itaconate, bis(2-hydroxyethyl)itaconate, bis(2-hydroxyethyl)fumarate, bis(2-hydroxyethyl)-maleate, 2-hydroxyethylvinyl ether, hydroxymethyl-vinylketone, allyl alcohol, etc. may be illustrated. Among these, hydroxymethyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl-(meth)acrylate, 3-hydroxypropyl(meth)acrylate, 3-phenoxy-2-hydroxypropyl(meth)acrylate, glycerolmono(meth)acrylate, hydroxybutyl(meth)acrylate, hydroxyhexyl(meth)acrylate, hydroxyoctyl-(meth)acrylate, hydroxymethyl(meth)acrylamide, 2-hydroxypropyl(meth)acrylamide, 3-hydroxypropyl(meth)acrylamide, etc. are preferred.
As the alkoxysilyl group-containing vinyl-based monomer, for example, the alkoxysilyl group-containing vinyl-based monomers disclosed in Japanese Unexamined Patent Publication (Kokai) No. 7-188356, such as trimethoxyvinylsilane, triethoxyvinylsilane, 6-trimethoxysilyl-1,2-hexene, p-trimethoxysilylstyrene, methacrylate-3-trimethoxysilylpropyl, acrylate-3-triethoxysilylpropyl, etc. may be mentioned.
As the carboxyl group, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, etc. may be mentioned.
As the polymer having a polar group containing a hetero atom and a benzene ring used in the present invention, a polymer having said amino group and benzene ring, preferably a polymer having a pyridine ring and benzene ring in its molecule, particularly preferably rubber latexes of these polymers are suitably used.
As the polymer having a carboxylic acid used in the present invention, for example, polyacrylic acid, an ethylene-vinyl acetate copolymer (including some carboxylic acids), polyamide, epoxy resins, polyester carboxylic acid-containing diene-based rubber, carboxylic acid-containing thermoplastic elastomers, carboxylic acid modified polyethylene, carboxylic acid-modified polypropylene, carboxylic acid-modified SEBS, etc. may be mentioned.
As the polymer having such a carboxylic acid, an elastomer (here, an xe2x80x9celastomerxe2x80x9d meaning a polymer having a glass transition point of less than room temperature) is preferred. As such an elastomer, for example, an acryl rubber, ethylene acryl rubber, carboxylic acid-modified polybutadiene, carboxylic acid-modified polyisoprene, carboxylic acid-modified nitrile butadiene rubber, carboxylic acid-modified butyl rubber, carboxylic acid-modified urethane rubber, carboxylic acid-modified silicone rubber, carboxylic acid-modified polysulfide rubber, carboxylic acid-modified fluororubber, carboxylic acid-modified epichlorohydrin rubber, carboxylic acid-modified norbornene rubber, carboxylic acid-modified styrene-based thermoplastic elastomer, carboxylic acid-modified olefin-based thermoplastic elastomer, carboxylic acid-modified urethane-based thermoplastic elastomer, carboxylic acid-modified polyester-based thermoplastic elastomer, carboxylic acid-modified polyamide-based thermoplastic elastomer, carboxylic acid-modified vinyl chloride-based thermoplastic elastomer, carboxylic acid-modified fluorine-based thermoplastic elastomer, etc. may be used.
Further, as the elastomer having a carboxylic acid, a carboxylic acid-containing latex is particularly preferred. As such a latex, for example, a styrene-butadiene-(meth)acrylate copolymer latex, styrene-butadiene-(meth)acrylate-vinylpyridine copolymer latex, carboxylic acid-modified liquid isoprene rubber latex, carboxylic acid-modified isoprene rubber latex, carboxylic acid-modified styrene-butadiene rubber latex, carboxylic acid-modified natural rubber latex, carboxylic acid-modified butadiene rubber latex, carboxylic acid-modified acrylonitrile-butadiene rubber latex, carboxylic acid-modified chloroprene latex, carboxylic acid-modified acryl rubber latex, carboxylic acid-modified acrylate-butadiene rubber latex, carboxylic acid-modified vinyl acetate rubber latex, etc. may be mentioned.
Further, the silica used in the present invention may be, not particularly limited to, a wet or dry silica, colloidal silica, surface-treated silica, etc. Any silica having residual silanol groups may be used.
The silica-polymer composite of the present invention can be obtained by reacting a predetermined polymer having a polar group containing a hetero atom and a benzene ring or a polymer having a carboxylic acid with silica in a solution in a one-step or two-step operation. In the case of a predetermined polymer component having a polar group containing a hetero atom and a benzene ring, the hetero atom-containing polar group unit and, in the case of a polymer having a carboxylic acid, the carboxylic acid unit must be reacted with the silica in an amount of more than 0.1 wt %. If the amount of the polymer component blended is not more than 0.1 wt %, separation ends up occurring and the desired silica-polymer composite cannot be obtained. The reaction time can be shortened along with rising in the reaction temperature. With a reaction at room temperature, a reaction time of at least 1 hour is required. Further, the polymer solution added second is not particularly limited, but an emulsion solution is preferred. Various ones such as SBR, BR, IR, NR, NBR, ABS, acrylate-based, and vinyl chloride-based ones may be used. Further, it is more preferred if an emulsifier, silane coupling agent, various oils, an antioxidant, a filler, plasticizer, softening agent, and other additives are present in the system.
The predetermined silica-polymer composite of the present invention, when kneaded in rubber as a reinforcing silica rubber master batch, can give a rubber composition which is low in viscosity during kneading with rubber, is excellent in processability, and is superior in dispersibility as well. The rubber component to be blended in the rubber composition according to the present invention is a cross-linkable rubber component and may be one component or a mixture of two or more. As the cross-linkable rubber, any rubber may be used. For example, natural rubber (NR), various types of butadiene rubbers (BR), various types of styrene-butadiene copolymer rubbers (SBR), polyisoprene rubber (IR), butyl rubber (IIR), acrylonitrile butadiene rubber, chloroprene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber, styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, chorosulfonated polyethylene, acryl rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluororubber, urethane rubber, etc. may be used. When using a blend, the blending ratio is not particularly limited.
The rubber composition according to the present invention may have blended in it various additives generally blended for general rubber use, for example, carbon black as a filler and further an ordinary vulcanization or cross linking agent, a vulcanization or cross-linking accelerator, various types of oils, an antioxidant, filler, plasticizer, softening agent, etc. The formulations may be kneaded and vulcanized by general methods to form a composition and used for vulcanization or cross-linking. The amounts of these additives blended may be the amounts generally blended in the past so long as they do not run counter to the objects of the present invention.
Below, the present invention will be explained further using Synthesis Examples, Examples, and Comparative Examples, but the scope of the present invention is of course not limited by these Examples.